Date: Wed, 19 Jan 2011 13:11:01 -0500 From: Jung-uk Kim <jkim@FreeBSD.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r217587 - head/sys/i386/i386 Message-ID: <201101191311.03440.jkim@FreeBSD.org> In-Reply-To: <20110119171807.GA2518@deviant.kiev.zoral.com.ua> References: <201101191709.p0JH97ZD083132@svn.freebsd.org> <20110119171807.GA2518@deviant.kiev.zoral.com.ua>
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On Wednesday 19 January 2011 12:18 pm, Kostik Belousov wrote: > On Wed, Jan 19, 2011 at 05:09:07PM +0000, Jung-uk Kim wrote: > > Author: jkim > > Date: Wed Jan 19 17:09:07 2011 > > New Revision: 217587 > > URL: http://svn.freebsd.org/changeset/base/217587 > > > > Log: > > Fix yet another fallout from r208833. VM86 BIOS call may cause > > page fault when FPU is in use. > > > > Reported by: Marc UBM Bocklet (ubm dot freebsd at googlemail > > dot com) Tested by: b. f. (bf1783 at googlemail dot com) > > MFC after: 3 days > > > > Modified: > > head/sys/i386/i386/vm86bios.s > > > > Modified: head/sys/i386/i386/vm86bios.s > > ================================================================= > >============= --- head/sys/i386/i386/vm86bios.s Wed Jan 19 > > 17:04:07 2011 (r217586) +++ head/sys/i386/i386/vm86bios.s Wed Jan > > 19 17:09:07 2011 (r217587) @@ -73,10 +73,9 @@ > > ENTRY(vm86_bioscall) > > je 1f /* no curproc/npxproc */ > > pushl %edx > > movl TD_PCB(%ecx),%ecx > > - addl $PCB_SAVEFPU,%ecx > > - pushl %ecx > > + pushl PCB_SAVEFPU(%ecx) > > call npxsave > > - popl %ecx > > + addl $4,%esp > > popl %edx /* recover our pcb */ > > 1: > > popfl > > vm86_bioscall() in fact inlines the old version of npxexit(). > Shouldn't the npxexit() be called from C code before call to > vm86_bioscall ? I think we can but I don't like redundant or nested uses of critical_enter()/critical_exit() from vm86_intcall()/vm86_datacall(). And I don't think that's worth the code churn. > Also, if bioscall can be used from the syscall context, I think > whatever npxsave()/npxexit() is used, and BIOS modifies FPU > state, we are corrupting usermode FPU context. > > Probably, fpu_kern_enter()/fpu_kern_leave() braces around > vm86_bioscall is proper solution. BIOS should never modify FPU state, AFAIK. Jung-uk Kim
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